Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$236.56	9.364%	$258.7115	$258.71	$258.70	$258.70
Purchase #2	$165.35	12.243%	$185.5938	$185.59	$185.60	$185.60
Purchase #3	$62.94	5.861%	$66.6289	$66.63	$66.65	$66.60
Purchase #4	$35.45	3.837%	$36.8102	$36.81	$36.80	$36.80
Purchase #5	$42.57	3.103%	$43.8909	$43.89	$43.90	$43.90
Purchase #6	$31.98	8.577%	$34.7229	$34.72	$34.70	$34.70
Purchase #7	$222.81	9.558%	$244.1062	$244.11	$244.10	$244.10
7 purchase totals =	$797.66		$870.4644	$870.46	$870.45	$870.40